Interfacial Lignin–MontmorilloniteFillersto Strengthen Biodegradable Polyester Packaging Films

Abstract Conventional petroleum-based food packaging plastics cause serious environmental pollution, driving demand for high-performance, fully biodegradable green packaging materials. Blends of poly(butylene adipate-co-terephthalate) (PBAT) and poly(propylene carbonate) (PPC) are promising alternatives for eco-friendly food packaging due to good flexibility, film-forming performance, and biodegradability. Nevertheless, poor gas-barrier, mechanical, and UV-shielding properties restrict their practical applications. In this study, quaternized alkali lignin (QAL) and alkyl-grafted quaternized lignin (QAC) were assembled with organo-montmorillonite (OMMT) to prepare quaternized alkali lignin-organo-montmorillonite (QAL-OM) and alkyl-grafted quaternized lignin-organo-montmorillonite (QAC-OM) hybrid fillers, which were added into the PBAT/PPC matrix at low contents. Benefiting from the UV absorption of lignin and the physical barrier of OMMT platelets, the modified composites exhibited enhanced mechanical barrier and UV-shielding performances with retained processability. At 0.7 wt % filler content, the oxygen permeability of PBAT/PPC/QAL-OM and PBAT/PPC/QAC-OM films was reduced by 25.71% and 27.11% to 71.46 and 70.11 cc·mm/(m2·day), respectively; their water vapor permeability decreased by 24.12% and 38.16% to 1.73 and 1.41 g·mm/(m2·day), respectively. QAC-OM showed better barrier performance because its long alkyl chains promoted OMMT intercalation and formed compact interfacial structures. Fruit preservation tests on bananas and litchis verified that the composite films retarded fruit deterioration and weight loss, proving great potential for biodegradable food packaging.